Characterization of thermotolerant, fermentative yeasts from hot spring drainage
Eight thermotolerant, ethanol-producing yeast strains were isolated from hot spring drainage at Rendaiji in Shizuoka Prefecture. The tolerance to elevated temperatures of three strains (RND13, 14 and 17) was studied in comparison with that of mesophilic yeasts. All three grew on a liquid culture at temperatures up to 42–45°C, with maximum growth rates at 37°C or 35°C, whereas the upper limit temperatures for fermentation were higher, ranging from 48 to 55°C. Above all, RND13 had higher ethanol productivity of 72.1% at 40°C for 24 h than that of 57.0% obtained by brewers' yeast at 25°C for 120 h. Regarding the taxonomy of RND13, 14, and 17, they were found to be Torulaspora delbrueckii, Dekkera sp., and Candida albicans, respectively. This is the first report on yeasts capable of fermentation over 51°C, as well as on the isolation of yeasts from a hydrosphere with elevated temperatures.